1. Field of the Invention
This invention relates to an improvement in an internal combustion engine provided with an engine cooling system, to prevent engine knock from arising particularly when engine operation is shifted to a high engine load mode.
2. Description of the Prior Art
In connection with water-cooled internal combustion engines, engine cooling is in general accomplished in such a manner that heat generated by the engine is transferred to circulating cooling water which absorbs the heat, and the thus absorbed heat is released to ambient air through a radiator under the influence of cooling air flow. In the engines of the above-mentioned type, it is known that the upper limit of the cooling water is controlled in accordance with engine load in order to reduce the loss in engine power output and improve engine driveability.
However, in the thus arranged engines, engine knock tends to arise immediately after the engine operation is shifted to a high engine load mode. In order to prevent this engine knock, it has been proposed to retard ignition timing, for example, by means of a vacuum advance mechanism; however, this allows a continuous ignition timing retardation throughout the high engine load mode operation, thereby deteriorating fuel economy and engine driveability after the engine cooling has sufficiently progressed, to the point where there is no possibility of raising engine knock.